As recorded in previous papers(1,2), griseolutein inhibited the growth of gram-positive bacteria and a few gram-negative bacteria at 0.1-2.0 mcg/ml and its minimal lethal dosis to mice by subcutaneous injection was larger than 1,600 mg/kg. The bacteriostatic effect and the low toxicity suggested that griseolutein was one of hopeful antibiotics. Serum and cysteine lowered the bacteriostatic effe...